Material-removing scraper with an articulated boom

ABSTRACT

A material-removing scraper with a scraping jib movable up and down by means of an elevating unit which consists of an articulated boom of flexibly jointed boom parts, tiltable relative to each other in a vertical plane, in which one delivers the bulk material to be removed from the pile or dump to the other in the area of the hinge connection. Means forcibly hold the delivery end of the one boom part above the receiving end of the other.

United States Patent inventor Gerhard Fischer Dortmund-Kirchhorde, Germany Appl. No. 867,131

Filed Oct. 17, 1969 Patented Nov. 23, I971 Assignee Gustav Schade Maschinenfabrik Dortmtind, Germany Priority Oct. 19, 1968 Germany P 18 04052.3

MATERIAL-REMOVING SCRAPER WITH AN ARTICULATED BOOM 16 Claims, 6 Drawing Figs.

0.8. Ci 198/36, 37/192 A, 198/92, 214/10 Int. Cl 865g 59/00 Field Search... 198/9, 36,

87.92, l74;2l4/10; 37/191 R, I92 R, [92A [56] References Cited FOREIGN PATENTS 680,544 8/1939 Germany... 37/192 R 747,683 10/1944 Germany 37/192 A Primary Examiner-Gerald M. Forlenza Assistant Examiner-Frank E. Werner A!lorney--Meyer, Tilberry and Body ABSTRACT: A material-removing scraper with a scraping jib movable up and down by means of an elevating unit which consists of an articulated boom of flexibly jointed boom parts. tiltable relative to each other in a vertical plane. in which one delivers the bulk material to be removed from the pile or dump to the other in the area of the hinge connection. Means forcibly hold the delivery end of the one boom part above the receiving end of the other.

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IN VEN TOR GER/1A RD F/SCHER AT7URNEYS BACKGROUND Material-removing scrapers heretofore have generally had a single, rigid scraping jib, although-it'has been suggested that the scraping jib be subdividedin alongitudinal direction "so that two scraping jibs, each of which is provided with its own driving gear, are arranged in series and so associated -with' each other thatthe front scraping jib, as seen in the direction of the conveyance, works on one side of the pile or on the upper side of the dump and the rear scraping jib works .on the otherside of the material pile. The two scraping jibs arranged in tandem are adjustable, as far as elevation ,and angular setting are concemed,by means of ropepulls, so that'the entire pile can be covered in its-full height and width and all the dumped material removed.

in one of the known material-removing scrapers of this kind, the'front part of the articulated jib is held and guided at its head end in aswivel bearing of a gantry crane. In the stretched position of the articulated jib, the boom parts lie in a straight line, one behind the other; the chain drums of the boom parts are thus located in the area of themoving joints, more or less spaced one behind the other. Heretofore this has lead to difficulties in the delivery" of the material to be transported from the front jib part to the rear jib part. The difficulty exists especially if a heavily caked or hardened material has to be removed, like for instance fertilizer, salt, etc.

A particular disadvantage of the known hinged connections is that the boom parts, when they are lowered about halfway to the bottom of the heap, i.e. in a stretched positionin which their longitudinal axes lie in a common, almost horizontal straight line, have their reversing endsat about the same level. [n this case, wedged deposits'of the bulk material can accumulate between these reversing ends of the boom parts which are not pickedEup by the scraping'elements ofthe rear boom parts and impair an.orderly transfer of' the material from-the front boom part to the rear boom part. The danger also exists in such a case that the scraping elements of the front boom part continueto carry the material along at the-reversing pointup to the upper portion of the boom part and carry it back again in this upper portion. The front boom part of the articulated jib works then in an unintentional short circuit without being able to deliver the material removed by it to the rear boom part. 1

THE INVENTION The invention is based onthe task of clearing away the difficulties encountered in material-removing scrapers provided with articulated booms by simple constructional means.

The two boom parts of the articulated boom are, according to the invention, coupled by a jointed step connection-or the like with the help of which the front boompart is held and adjustable with its endfacing the jointed connection at a level above the adjacent end of the other, rear boom part.

The mentioned step connection can in a very simple constructional arrangement consist of arms or the like which are rigidly connected with one boom part, inclined to its longitudinal axis, and flexibly connected with the other boom part. The use of angle arms is particularly advantageous when one end is rigidly joined to one boom part and the other end is flexibly connected at its extremity to-the other boom part of the articulated boom.

The underlying idea of the invention consists according to this in that the two boom parts lying in a common vertical plane are so connected at their linkage point that the front boom part in every operational position including the stretched position, is forcibly held with its reversing end adjacent the linkage point, so far above the adjacent reversing end of the rear boom part that the formation of wedged material deposits is prevented and the scraping rakes of the front boom part dump the material, heretofore taken along by them as they went around the reversing end, without bindrance over a step forming on the surface of the dump at the linkage point in the delivery area of the scraping rakes of the rear boom part, so that it can betaken along by the latter.

in this construction of the flexible connection the front boom part can thus not be lowered to a position in which it lies in an exactly straight line with the rear boom part. This means that in the working area of the front boom part a step of the bulkmaterial results at the bottom of the dump which cannot be cleared by the front boom part. However, if this cannot be tolerated, the removal of the remaining step is in case of necessity easily possible, for instance with the help of a tractor grader. On the other hand, it is also possible to provide the bottom of the dump with an appropriate step.

Howevenin order to remove also this step of remaining material with the help of the front boom part and/or to adjust the difference of elevation by which'the front boom part is positioned with its reversing end above the adjacent reversing end of the rear boom part, the step connection can, according to another characteristic of the invention, consist of two hinges with parallel swivel axis. The two boom parts are in this case appropriately suspended on two separate elevating units which can be so controlled that the two boom ends facing the swivel connection are elevated to different levels in relation to each other. it is advisable to fasten the hoisting rope of the elevating device belonging to the front boom partof this part near the flexible connection and to assign additionally. another elevating device to thisboom part whose rope engages its intermediate or front section.

The step connection is, according to a further characteristic of the invention, provided with two hinges with parallel swivel axes one of which can be rigidified or made fixed. If both hinges are movable, the front boom part can be lowered to a position in which it lies in a straight line with the rear boom part. In this case it is thus possible to clear also the step remainingon the bottom of the dump underneath the front boom part. Making the aforementioned hinge rigid can be accomplished for instance by means of a locking bolt, a latch or any other means. On the other hand, the. locking of the hinge can also beeffected by means of an extensible device which has at the same time the task of adjusting the elevation of the twoboom parts in relation to each other and which may consist for'instance of a spindle or screw drive but preferably is however a piston cylinder device actuated by a pressure medium.

The step connection consists in this last-mentioned construction preferably of intermediate connecting links which are connected with one boom part by means of the hinge which can-be rigidified or fixed and which pivotally engage the rigidly arranged arms on the end of the other boom part. For making the intermediate connecting links rigid, a mechanical drive or an extensible device actuated by a pressure medium can be used, as mentioned above, with the help of which the intermediate inks of the connection can be locked.

With regard to the construction, one design is of particular advantage in ivhich the intermediate connecting links consist of approximately triangular plates which are pivotally or flexibly connected with one of the triangular points to the one boom part and also to the other boom part, whereas the third triangular point is engaged by the pivot drive or extensible device. It is advisable to connect the intermediate links flexibly with the rear boom part carrying the pivot drive, while the front boom part carries the rigid arms which are flexibly connected with the intermediate links.

OBJECTS The principal object of the invention is an arrangement for pivotally or flexibly connecting the boom parts of a materialremoving scraper such that feeding of material from one part to the other part is always assured.

Another object is an arrangement whereby the reversing end of one boom part is always held above the reversing end of another boom part to which it is delivering material regardless of the angular position of the boom parts.

Still another object is the provision of an arrangement whereby the step which forms between the two boom parts can be removed.

Another object is the provision of an arrangement whereby the problem of material being carried around the end of one boom part and back along the top is prevented.

DRAWINGS Examples of practical applications of the invention are represented in the drawings which are a part hereof and wherein:

FIG. I shows the ends of two boom parts of an articulated jib in side view in the area of their hinged connection, the articulated jib being in a stretched position in which the boom parts are lying in a common plane;

FIG. 2 is similar to FIG. 1 in which, however, the two boom parts are staggered, as far as their elevation is concerned, at their reversing ends;

FIG. 3 is a material-removing scraper with an articulated jib in side view which is equipped with a step connection according to the invention;

FIG. 4 and 5 are modified designs of the step connection according to the invention in a lateral view and in top view respectively;

FIG. 6 is third embodiment of the invention.

PREFERRED EMBODIMENT In FIG. 1 the two boom parts of an articulated jib are designated with l and 2. The two boom parts I and 2 consist in a known construction of a frame 3 which is generally built as a box girder by welding. Shafts are pivoted at the end of the frame which carry chain wheels 4 for the parallel endless chains 5 which are connected with each other by appropriately spaced scraping rakes 6. The chains 5 revolving in the longitudinal direction of the two boom parts I and 2 are driven by means of a driving mechanism (not shown) which operates the shaft of a chain wheel. However, each of the two boom parts has its own drive.

In FIG. I the joint in the area of the reversing ends of the boom parts 1 and 2 is not distinctly shown. The two boom parts are shown in one common vertical plane, in a stretched position and in end to end relationship, so that their longitudinal axes are in alignment. The front scraping jib 2 transports the bulk material piled on the dump 7 in the direction of the arrow S and transfers it at the linkage point to the rear boom part 1 which transports the material also in the direction of the arrow S. Especially if the bulk material is sticky or if it has a tendency to cake, a wedge 8 of the bulk material can build itself up in the area of the joint which cannot be picked up and removed by the scraping rakes 6 revolving around the chain wheels 4. This has the result that the scraping rakes 6 of the front boom part 2, instead of transporting the bulk material 7' to the area to be cleared by the scraping rakes of the rear boom part I, convey it to the area of the joint, and then at least partly, upwardly on the previously deposited wedge and then back on the upper portion of the front boom part. An orderly transfer of the bulk material from the front boom part 2 to the rear boom part I is therefore not possible.

In accordance with the invention and as shown in FIG. 2, the reversing end of boom part is offset vertically above the reversing end of boom part I, so that a step 7" is formed on the dump at the point of connection and transfer. Since the reversing end of the front boom part 2 lies above the reversing end of the boom part 1 by about the height of the jib or boom part, the scraping rakes 6 of the front boom part 2 can without difficulty while revolving around the reversing end dump the bulk material 7' carried along by them down into the operational area of the scraping rakes of the rear boom part 1, so that it can be removed by the latter.

The result of this comparison of the FIG. 1 and 2 is therefore that it is essential for a trouble free transfer of the bulk material from the front boom part 2 to the rear boom part 1 that the reversing end of the front boom part be held at a certain distance above the reversing end of the rear boom part 1.

In FIG. 3 a material-removing scraper is shown in which the articulated jib K is suspended. movable up and down, on a gantry crane 9 which extends over the entire pile of bulk material 7 and is of a trapezoid cross section and which travels on parallel tracks 10 which are placed on both sides of the dump in its longitudinal direction. The rear boom part I of the articulated jib is pivoted on the gantry crane 9 in a swivel bearing 11 near the base of the dump swingable around a horizontal axis. The front boom part 2 is suspended by means of a hoisting ropes I2 and two hoists or winches 13. It is thus possible to lower the articulated jib by means of the two hoists I3 from the position shown in the dashed outline to the fully stretched position in which the two boom parts clear the dump completely with the exception of the step 14 remaining underneath the boom part 2.

The two boom parts I and 2 are in the area of the joint 15 linked with each other i.e. movably hinged by means of two parallel angle arms 16. The angle arms 16 have one of their sides or ends rigidly fastened to the lateral surfaces of the boom part 2, whereas the other end is inclined downwardly with regard to the longitudinal axis of the boom part 2 and hinged the rear boom part 1 by means of a joint 17. Such a construction of the pivoted linkage using angle arms which are rigidly fastened at one end to the front boom part 2 above the linkage point on boom part 1 results in this end of the boom part 2 being forcibly held in all positions of the boom part 2 at a certain distance above the adjacent end of the boom part I, as shown in FIG. 2.

The same effect could be achieved if in place of the angle arms 16, nonangled or straight arms were used which are rigidly fastened to the front boom part 2 in the shown sloping position and with their other end hinged to the rear boom part I. It is also possible to fasten the arms or the angle arms I6 respectively in the shown sloping position rigidly on the rear boom part 1, and hinge or pivot them to the front boom part 2. In all cases the arrangement makes certain that in all operational positions of the two boom parts, a satisfactory and complete transfer of the bulk material from the font boom part 2 to the rear boom part 1 is achieved.

With this construction, a step I4 always remains underneath the front boom part 2 which cannot be removed by this boom part, since the boom part cannot be completely lowered to the level of the rear boom part 1. This step 14 can be cleared, if so desired, by means of another device, for instance a tractor grader. However, it is also possible to provide this step to begin with at the time the dumping ground is built by constructing it for instance of concrete.

In the embodiment of the invention shown in FIGS. 4 and 5, intermediate links 20 in the form of triangular plates are laterally pivoted in swivel bearings 21 with a common axis 22 on the end of the rear boom part I. The front boom part 2 has rigid arms 23 fixed to its sides which at the other end are hinged at 24 to the intermediate links 20. On the two lateral surfaces of the boom part 1, hydraulic cylinders 25, one on each side, are pivoted to a swivel bearing 26. Piston rods 27 associated with the hydraulic cylinders are coupled with the remaining point of the triangle of the plates 20 by means of a hinge 28. Stops 29 on the lateral surfaces of the boom part 1 limit the swinging motion of the intermediate links 20 in the retracted position piston rods 27.

In the position shown, the hinges 21 of the intermediate links 20 can be held in position by the cylinders 25 whose piston rods are prevented from sliding out in a known manner. The reversing end of the front boom part 2 is thus kept in the shown position at a certain distance above the reversing end of the rear boom part 1. This position is normally maintained during the operation, in which setup the front boom part 2 can however swing around the hinge axis 24 in the course of the clearing operation. The elevation adjustment in relation to each other of the ends of the boom parts can, if necessary, be adapted to the bulk material in question by moving the piston rod out of the adjusting cylinder 25 to a certain extent. When the end position, shown fully outlined in FIG. 3, ofthe articulated jib K is reached, in which phase of the operation, a step M of the bulk material has been formed underneath the front boom part 2, the piston rods of the swiveling cylinder 25 can be moved out. The plate-shaped intermediate links 20 swing around the hinges 21 in the direction of the arrow P until they occupy a position in which the front boom part 2 lies in the same plane a is the rear boom pan; 1. This position is indicated in FIG. 4 in a dashed outline. It is thus possible to remove the step 14 of the bulk material completely.

in place of the hydraulic cylinder 25 other devices can, of course, also be used, e.g., lever drives or spindle or screw drives, etc. it is also possible to lock the intermediate links 20 in the normal operating position shown in FIG. 4 and prevent their moving in the direction of the arrow P by means of other devices, e.g. locking bolts, latches, etc.

in the embodiment of the invention shown in FIG. 6, which corresponds in its basic construction to that shown in FIG. 3, the two boom parts I and 2 are coupled at the linkage point 15 by means of an intermediate link 16', consisting of a pair of arms, which are connected with both boom parts land 2 by means of hinges 17. The horizontal axes of these two hinges are parallel to each other. The intermediate link 16 may also consist of hinged brackets or the like. The elevating device of this articulated jib has three hoisting units 13 and 13'. The hoisting rope 12' of the hoist 12' engages the rear boom part 1 in the proximity of the hinged connection 15, while one of the two hoists l3 acts on the front boom part 2 through its hoisting rope 12 near the hinge connection 15. The hoisting rope of the other hoist 13 is fastened in this set up to the forward section of the boom part 2, Le. remote from the hinged connection 15.

With such an arrangement it becomes thus possible to lower the two boom parts 1 and'2 in the course of the removal of the bulk material from the pile from the position shown in a dashed outline to the fully outlined position by an appropriate control of the hoists l3 and 13 in such a manner that the end of the front boom part 2 lying at the linkage point 15 takes on a position above the adjacent end of the boom part over the entire field of traverse of the articulated jib. This end of the boom part 2 can then be lowered by extending the hoisting rope l2 engaging this end so far that also the step 14 is removed.

I claim:

1. A material-removing scraper including scraper jib means mounted for substantially vertical up and down movement, elevating means for moving said jib means substantially vertically up and down, said scraper jib means comprising an articulated boom including first and second boom parts, said first and second boom parts having longitudinal axes and adjacent boom ends positioned adjacent one another, flexible connection means flexibly connecting said adjacent boom ends for tilting movement of said first and second boom parts relative to one another in a substantially vertical plane, said flexible connection means connecting said boom ends for positioning of one of said adjacent boom ends at a level above the other of said adjacent boom ends, said connection means comprising arm means rigidly connected with one of said boom parts and extending away therefrom at an angle to its longitudinal axis, said arm means being flexibly connected with the other of said boom parts.

2. A material-removing scraper including scraper jib means mounted for substantially vertical up and down movement, elevating means for moving said jib means substantially vertically up and down, said scraper jib means comprising an articulated boom including first and second boom parts, said first and second boom parts having longitudinal axes and adjacent boom ends positioned adjacent one another, flexible connection means flexibly connecting said adjacent boom ends for tilting movement of said first and second boom parts relative to one another in a substantially vertical plane, said flexible connection means connecting said boom ends for positioning of one of said adjacent boom ends at a level above the other of said adjacent boom ends, said connection means including rigid member means connected with each of said boom parts by movable hinge joint means having parallel swivel axes, and rigidifying means for rigidifying at least one of said movable hinge joint means.

3. The device of claim 2 wherein said connection means includes an intermediate link pivotally connected with one of said boom parts, adjustable locking means for selectively locking said intermediate link in-a plurality of pivoted positions, and arm means pivotally connected to said intermediate link and rigidly connected to the other of said boom parts.

4. The device of claim 3 wherein said adjustable locking means comprises a mechanical lock.

5. The device of claim 3 wherein said intermediate link comprises a substantially triangular plate having a plurality of triangular points, said plate being pivotally connected with said arm means at one of said triangular points and to said one boom part at another of said triangular points, and extensible means connected with a third of said triangular points.

6. The device of claim 3 wherein said adjustable locking means comprises a hydraulic cylinder and piston pivotally connected with said intermediate link and one of said boom parts.

7. A material-removing scraper including scraper jib means mounted for substantially vertical up and down movement, elevating means for moving said jib means substantially vertically up and down, said scraper jib means comprising an articulated boom including first and second boom parts, said first and second boom parts having longitudinal axes and adjacent boom ends positioned adjacent one another, flexible connection means flexibly connecting said adjacent boom ends for tilting movement of said first and second boom parts relative to one another in a substantially vertical plane, said boom parts being lowerable to a substantially lowermost position in which said longitudinal axes extend in substantially straight elongation of one another, said flexible connection means connecting said boom ends for positioning of one of said adjacent boom ends at a level above the other of said adjacent boom ends when said boom parts are substantially in said lowermost position.

8. The device of claim 7 wherein said boom parts have opposite boom ends remote from said adjacent boom ends, said opposite boom ends being positioned below said one boom end when said one boom end is positioned at a level above the other of said boom ends.

9. A material-removing scraper including scraper jib means mounted for substantially vertical up and down movement, elevating means for moving said jib means substantially vertically up and down, said scraper jib means comprising an articulated boom including first and second boom parts, said first and second boom parts having longitudinal axes and adjacent boom ends positioned adjacent one another, flexible connection means flexibly connecting said boom ends for tilting movement of said first and second boom parts relative to one another in a substantially vertical plane, said flexible connection means connecting said boom ends for positioning of one of said first and second boom parts in a first plane and for positioning the other of said boom parts in a second plane substantially parallel to said first plane and located above said first plane so that said boom end on said other boom part is displaced to a level above said boom end on said one boom part when said boom parts are in substantially parallel positions.

10. The device of claim 9 wherein said other of said boom parts has an opposite boom end opposite said adjacent boom end thereof, said opposite boom end on said other boom part being positioned below said adjacent boom end thereof when said adjacent boom end is at a level above said boom end on said one boom part.

11. The device of claim 9 wherein said connection means comprises a rigid member connected with each of said boom parts by a movable hinge joint, said hinge joints having parallel swivel axes.

12. The device of claim 111 wherein said elevating means comprises a plurality of separate hoisting units, each of said boom parts being connected with a separate one of said hoisting units whereby selective operation of said hoisting units adjustably positions said adjacent boom ends at various levels relative to one another.

13. The device of claim 12 wherein one of said hoisting units is connected with one of said boom parts adjacent said adjacent boom end thereof and another of said hoisting units is connected with said one boom part at a point remote from said adjacent boom end thereof.

14. The device of claim 9 and further including rigidifying means for rigidifying said connection means.

15. The device of claim 9 wherein said connection means 

1. A material-removing scraper including scraper jib means mounted for substantially vertical up and down movement, elevating means for moving said jib means substantially vertically up and down, said scraper jib means comprising an articulated boom including first and second boom parts, said first and second boom parts having longitudinal axes and adjacent boom ends positioned adjacent one another, flexible connection means flexibly connecting said adjacent boom ends for tilting movement of said first and second boom parts relative to one another in a substantially vertical plane, said flexible connection means connecting said boom ends for positioning of one of said adjacent boom ends at a level above the other of said adjacent boom ends, said connection means comprising arm means rigidly connected with one of said boom parts and extending away therefrom at an angle to its longitudinal axis, said arm means being flexibly connected with the other of said boom parts.
 2. A material-removing scraper including scraper jib means mounted for substantially vertical up and down movement, elevating means for moving said jib means substantially vertically up and down, said scraper jib means comprising an articulated boom including first and second boom parts, said first and second boom parts having longitudinal axes and adjacent boom ends positioned adjacent one another, flexible connection means flexibly connecting said adjacent boom ends for tilting movement of said first and second boom parts relative to one another in a substantially vertical plane, said flexible connection means connecting said boom ends for positioning of one of said adjacent boom ends at a level above the other of said adjacent boom ends, said connection means including rigid member means connected with each of said boom parts by movable hinge joint means having parallel swivel axes, and rigidifying means for rigidifying at least one of said movable hinge joint means.
 3. The device of claim 2 wherein said connection means includes an intermediate link pivotally connected with one of said boom parts, adjustable locking means for selectively locking said intermediate link in a plurality of pivoted positions, and arm means pivotally connected to said intermediate link and rigidly connected to the other of said boom parts.
 4. The device of claim 3 wherein said adjustable locking means comprises a mechanical lock.
 5. The device of claim 3 wherein said intermediate link comprises a substantially triangular plate having a plurality of triangular points, said plate being pivotally connected with said arm means at one of said triangular points and to said one boom part at another of said triangular points, and extensible means connected with a third of said triangular points.
 6. The device of claim 3 wherein said adjustable locking means comprises a hydraulic cylinder and piston pivotally connected with said intermediate link and one of said boom parts.
 7. A material-removing scraper including scraper jib means mounted for substantially vertical up and down movement, elevating means for moving said jib means substantially vertically up and down, said scraper jib means comprising an articulated boom including first and second boom parts, said first and second boom parts having longitudinal axes and adjacent boom ends positioned adjacent one another, flexible connection means flexibly connecting said adjacent boom ends for tilting movement of said first and second boom parts relative to one another in a substantially vertical plane, said boom parts being lowerable to a substantially lowermost position in which said longitudinal axes extend in substantially straight elongation of one another, said flexible connection means connecting said boom ends for positioning of one of said adjacent boom ends at a level above the other of said adjacent boom ends when said boom parts are substantially in said lowermost position.
 8. The device of claim 7 wherein said boom parts have oPposite boom ends remote from said adjacent boom ends, said opposite boom ends being positioned below said one boom end when said one boom end is positioned at a level above the other of said boom ends.
 9. A material-removing scraper including scraper jib means mounted for substantially vertical up and down movement, elevating means for moving said jib means substantially vertically up and down, said scraper jib means comprising an articulated boom including first and second boom parts, said first and second boom parts having longitudinal axes and adjacent boom ends positioned adjacent one another, flexible connection means flexibly connecting said boom ends for tilting movement of said first and second boom parts relative to one another in a substantially vertical plane, said flexible connection means connecting said boom ends for positioning of one of said first and second boom parts in a first plane and for positioning the other of said boom parts in a second plane substantially parallel to said first plane and located above said first plane so that said boom end on said other boom part is displaced to a level above said boom end on said one boom part when said boom parts are in substantially parallel positions.
 10. The device of claim 9 wherein said other of said boom parts has an opposite boom end opposite said adjacent boom end thereof, said opposite boom end on said other boom part being positioned below said adjacent boom end thereof when said adjacent boom end is at a level above said boom end on said one boom part.
 11. The device of claim 9 wherein said connection means comprises a rigid member connected with each of said boom parts by a movable hinge joint, said hinge joints having parallel swivel axes.
 12. The device of claim 11 wherein said elevating means comprises a plurality of separate hoisting units, each of said boom parts being connected with a separate one of said hoisting units whereby selective operation of said hoisting units adjustably positions said adjacent boom ends at various levels relative to one another.
 13. The device of claim 12 wherein one of said hoisting units is connected with one of said boom parts adjacent said adjacent boom end thereof and another of said hoisting units is connected with said one boom part at a point remote from said adjacent boom end thereof.
 14. The device of claim 9 and further including rigidifying means for rigidifying said connection means.
 15. The device of claim 9 wherein said connection means includes link means pivotally connected to each of said first and second boom parts, and adjustable locking means for adjustably locking said link means in a plurality of pivoted positions.
 16. The device of claim 9 wherein said connection means comprises rigid arm means rigidly connected to one of said boom parts and extending away therefrom at an angle to said longitudinal axis of said one boom part, said arm means being flexibly connected to the other of said boom parts. 